Photo printing machine with exposure control

ABSTRACT

A photo-printing machine has a light transmission measuring station with a control value forming device connected thereto. The control value is retained in a store and is utilized through a transfer regulator to control the drive speed of the mechanism carrying printing paper through the exposure station, thereby to control the exposure in accordance with the density of the material being printed.

United States Patent 1 lsermann [451 Sept. 4, 1973 PHOTO PRINTING MACHINE WITH EXPOSURE CONTROL [75] Inventor: Heinrich Isermann, Siegen,

Germany [73] Assignee: Meteor-Siegen Apparatehau Paul Schmeck Gmbl-I, Siegen, Germany [22] Filed: Apr. 6, 1972 [211 App]. No.: 241,564

[30] Foreign Application Priority Data Apr. 23, 1971 Germany P 21 19 869.6

[52] US. Cl. 355/83 [51] Int. Cl. G03b 27/78 [58] Field of Search 355/83, 64, 84, 103, 355/l08 [56] References Cited UNITED STATES PATENTS 3/1960 Blackmer 355/83 3,588,247 6/l97l Noda 355 33 1,925,355 9 1933 Whitson..... 355/83 3,472,592 10/1969 Nichols 355/83 3,642,377 2 1972 Young 355/83 Primary Examiner.lohn M. Horan Attorney-Olson, Trexler, Wolters & Bushnell [57] ABSTRACT A photo-printing machine has a light transmission measuring station with a control value forming device connected thereto. The control value is retained in a store and is utilized through a transfer regulator to control the drive speed of the mechanism carrying printing paper through the exposure station, thereby to control the exposure in accordance with the density of the material being printed.

8 Claims, 3 Drawing Figures PHOTO PRINTING MACHINE WITH EXPOSURE CONTROL The invention relates to a photo-printing machine and particularly to a photo-printing machine having a measuring station for measuring the transparency of an original to be printed, a store for a control value representing the transparency measured, an exposure station for the exposure of the material to be reproduced and a circuit for the drive for the said material, connected to the said store and conveying the said material through the exposure station at a speed dependent on the control value.

With a photo-printing machine of this type exemplified by German Pat. specificiation No. 1,522,790, the store is connected to the light measuring element of the measuring station and, when an original is measured, receives the electrical signals supplied by this latter, as a control value which constitutes a criterion of its translucency. This control value is represented by the voltage of a charged capacitor and, after amplification, is applied to regulate the speed of the drive of the material to be copied. The rotational speed of the drive is thus adjusted to ensure that a very transparent original, together with the printing paper, is fed forward, through the exposure zone with a constant light source, at a greater speed than an original presenting a greater resistance to light.

This transparency measuring and exposure regulation system suffers from a number of drawbacks. Above all, in the case of a rapid printing sequence, the copies are in many cases not evenly exposed, so that the original has to be printed again. This makes the production of a copy more time consuming and increases the consumption of paper. It is true that the uneven exposures can be counteracted, within certain limits, by maintaining a greater distance between the individual originals fed into the machine one after the other. This measure likewise, however, results in the consumption of increased time for each copy, so that the overall printing output of the machine, i.e., the maximum number of copies obtained per hour, is disproportionately reduced.

In accordance with the present invention, a photoprinting machine includes a measuring station for measuring the transparency of an original to be printed, a control value forming device connected to the measuring station and arranged to generate a control value signal, a store, an exposure station for exposing material to be reproduced, a drive for moving the material through the exposure station, a control circuit for the drive, arranged under the control of the store to vary the drive speed in accordance with a control value signal in the store, and a transfer regulator arranged to vtransfer a signal from the control value forming circuit to the store, when the material to be reproduced enters the exposure station.

The separation of the formation of the control value signal (in the control value forming circuit) from the control value store for the drive ensures that an original together with the printing paper passes the whole way through the exposure station at the correct rate of feed, regardless of whether or not a control value is already being formed for a subsequent original. When the latter enters the exposure station the preceding original will have already left it, so that the exposure of a first original cannot be influenced by the transfer of the control value signal formed for the second original to the store acting directly on the drive. The photo-printing machine to which the invention relates thus eliminates the possibility of faulty exposures arising from the control value for a subsequent original altering the rate of feed of the preceding original while the latter with its printing paper is still passing through the exposure station. A number of originals to be reproduced can pass through the machine in almost uninterrupted succession.

The control value former is advantageously provided with a capacitor connected via an electronic valve to the measuring station. The capacitor voltage representing the control value is prevented from falling if less transparent portions or black portions follow highly transparent portions during the transparency measurement of the original.

The electronic valve preferably consists of a MOS- FET (metal oxide silicon semi-conductor field effect transistor) which is controlled by a comparator and in which an extremely high blocking resistance is combined with the maximum transmitting resistance. The short response time of this circuit enables small zones of high transparency to be reliably measured even when the original is being fed forward at high speeds.

The response time is advantageously shortened still further by an amplifier which follows the capacitor and of which the output is connected to a comparator input.

Finally, the transfer regulator contains a motion pickup which causes the measured value to be transmitted from the control value former to the store, regardless of the speed at which the material to be reproduced is being fed through the machine, shortly before the original to which the control values enters the exposure station.

The invention will be more readily understood by way of example from the following description of a photo-printing machine in accordance therewith, reference being made to the accompanying drawings, in which:

FIG. 1 illustrates the machine schematically and shows the sequence of functions in the machine,

FIG. 2 is a schematic diagram of a circuit for the formation and storage of the measured value dependent on the transparency of the original, and

FIG. 3 is a schematic diagram of a circuit for adapting the drive rotation speed to a reduced control value.

When an original 2 is introduced into the photoprinting machine 1, its transparency is first of all measured in a measuring station 4. For this purpose a narrow beam of light 6 is diverted from a photo-printing light source 9 and guided through the original into a photo-sensitive device 5, which may be for example a photo-cell or photo-conductive cell.

The original 2 and the printing paper 3 cutto the correct length are brought together in front of the exposure station 8. The exposure station 8 is formed by a transparent gap which extends over the entire width of the original and which is provided in a cylinder which gives passage to. the photo-printing light source but which is otherwise impermeable to light, while the original, bearing the photo-printing paper on the side facing away from the cylinder, is moved past the latter at a rate of speed determined by the transparency of the original.

Beyond the exposure station the original and the exposed photo-printing paper are separated from each other, the original being delivered in a forward direction and the exposed photo-printing paper being conveyed to a developing station 10, from which it emerges towards the rear, in the form of a finished copy, after the developing process has been completed.

The formation of the control value dependent on the transparency of the original and also the control of the rate of feed through the exposure station are shown in a schematic circuit diagram in FIG. 2. The photosensitive device 5 from the measuring station 4 (FIG. 1) contains, as shown in FIG. 2, the photo-cell 20 which is subjected to radiation, through the original, from the beam of light 6 diverted from the printing light source, possibly after that beam has been adapted to the characteristic of the photo-printing paper used. The output of the photo-cell 20 is connected, via a switch S to the input A of the control value former I. In the control value former I a terminal of a MOSFET 22 is connected to the input A. The other terminal of the MOSFET is connected to a condenser 26, with which an operational amplifier 28, as well as a quenching circuit consisting of the switch 8, and the discharge resistor 29, are connected in parallel. The output of the operational amplifier 28 leads via an amplifier 30 to an input of a comparator 24 of which the other input is at the point A. The comparator 24 produces a certain preselected level at its output 25 when the voltage at the output B of the amplifier 30 is less than the voltage at A. This output level from the comparator 24 is coupled through separating transformer, having a high ohmic resistance to the control electrode (gate g) of the MOS- FET 22 and opens it from the input point A to the capacitor 26 as long as the voltage at A is greater than that at B.

The output B of the control value former I leads via a switch S, to a storage capacitor 36 in the store II, with which an operating amplifier 38 is connected in parallel. The store II is directly coupled with the drive 50 for the feed of the original and the printing paper through the photo-printing machine.

The switch S, is controlled by a transfer regulator 40 which, in its turn, is connected to the drive 50.

If an original 2 is inserted in the pnoto-printing machine its front edge crosses over a light barrier, for instance, at S (FIG. I) or operates a feeler or other control element, which in its turn closes the switch S, between the measuring station and the control value former I. The formation of the control value then commences. Before the switch S is actuated, capacitor 26 has been discharged by closing the switch 8; via the discharge resistor 29. At the commencement of the formation of the control value, however, the switch S, is always open.

If portions of the original which bear no text are eradiated by the beam of photo-printing light 6, the voltage at point A rises in relation to that at point B and the MOSFET 22 is opened by the output level of the comparator 24. The capacitor 26 charges up as long as the voltage at A remains greater than that at B. If less transparent portions of the original enter the path of the photo-printing light 6, the voltage A decreases in relation to that at B, the comparator 24 blocks the MOF- SET 22 and the capacitor 26 is prevented by the extremely high blocking resistance of the MOSFET from discharging, even if the original is being fed forward at a low speed. The charge state of the capacitor 26 therefore represents, at any given moment, that portion of the original with the maximum measured permeability to light.

The control value representing the transparency of the original is given by the output voltage at the point B which represents the voltage of the capacitor 26, amplified by the amplifier 30.

When a sufficient portion of the original has been measured for its transparency, the switch S, is opened and the control value retained in the control value former I until the front edge of the original has reached the commencement of the exposure zone 8. At this moment the transfer regulator 40 closes the switch S so that the control value is transmitted to the store II. The storage capacitor 36 in the store II charges up in accordance with the voltage at point B. The operational amplifier 38, the output voltage of which is the voltage of the storage capacitor 36, directly controls the drive 50 for the feed of the original and of the corresponding photo-printing paper. The rotational speed of the drive is thus set, immediately after the closing of the switch S in accordance with the, control value transmitted, so that the new original passes through the exposure station at the speed determined by its permeability to light.

After the control value has been transmitted from the control value former I to the store II the switch S is opened. Immediately prior to the next measuring operation the capacitor 26 in the control value former I is discharged through the resistor 29, by the temporary closing of the switch S The control value former I is thus in readiness for the acceptance of a new measured value, despite the fact that the preceding original is still passing through the exposure station.

The transfer regulator 40 is provided with a switching disc which is directly coupled with the feed drive and of which the periphery is determined by the distance covered by the front edge of the original from the beginning of the transparency measuring operation to the entry into the exposure. zone 8. This disc functions as a motion pick-up which is independent of the rate of feed and which always closes the switch S between the control value former I and the store II when the front edge of the original enters the exposure station 8. The switching disc could of course be replaced, in the vicinity of the exposure station 8, by a feeler which responds to the rear edge of the preceding original and photoprinting paper or to their front edge and which operates the switch S, accordingly.

When the control value is transmitted from the control value former I to the store II the rotation speed of the drive 50 for the material to be reproduced has to be adapted to the altered control value. If the new control value is appreciably lower than the preceding one, a great deal of time -is required for the said adaptation if the drive is only braked by the friction of the machine. lt is therefore advisable to provide for the purpose a special brake device as illustrated in FIG. 3.

This brake device is provided with a comparator 52 which compares the voltage at the output C (FIG. 2) of the store with a voltage U representing the rotation speed of the drive at the moment in question and which closes a switch S, for as long as the voltage at C is lower than U The switch S connects-the motor M of the drive to a load resistor 54.

These measures enable the correct rate of feed to be set without delay, even in the case of a considerably reduced control value.

FIG. 2 also shows, in the measurement" zone, a further circuit provided in order to adapt the measuring signal used for the formation of the control value to the photo-sensitivity characteristic of various types of photo-printing paper which can be used as desired. In the example shown there is a choice between three different types of photo-printing paper (of the three rolls indicated in FIG. 1). Each type of paper is associated with one of the three current paths bridging the amplifier 21. The degree of amplification of the amplifier 21 is obtained from the ratio between the resistance values of the resistors 60 and 61, on the one hand, and one of the three resistor combinations 62 and 63, on the other hand, any of these latter desired being switched on by means of the switches 64. The variable resistors 60 and 63 enable adjustment to be made to take into account the different properties of the photo-printing paper, on the one hand, and the particular basic shade desired in the copies, on the other.

When one of the three current paths bridging the amplifier 21 is switched in by means of one of the switches 64, which are associated with the selector switches for the types of printing paper and the appropriate one of which is automatically actuated on the selection of the type of printing paper, an actuating element in the form of a magnet 66 or 67 for the spectral sensitivity adaptation of the measuring light to the relevant type of photo-printing paper is switched on; the actuating element 66 or 67 energised is preselected by one of three switches 65. The actuating element 66 or 67 modifies, for example, the sets of diaphragms of a filter diaphragm system in the path of the measuring light and associated with the various band filters, and the filter diaphragm system serves to adapt the spectral sensitivity characteristic of the photo-cell to that of the photoprinting paper.

The invention is claimed as follows:

1. A photo-printing machine for printing copies of varying sizes from originals of correspondingly varying sizes, including a measuring station having a .photosensitive device for measuring the transparency of an original to be printed, a control value forming device and first store including a capacitor connected via an electronic valve to the photo-sensitive device of the measuring station to generate a control value signal, a second store for receiving a signal from the first store, an exposure station for exposing material to be reproduced, a drive for moving the material through the exposure station, a control circuit for the drive, arranged under the control of the stores to vary the drive speed in accordance with a control value signal in the second store, and a transfer regulator arranged to transfer a signal from the control value forming circuit and first store to the second store, when the material to be reproduced enters the exposure station.

2. A photo-printing machine according to claim 1, in which the electronic valve is a MOSFET of which the control electrode is connected via a separating trans former, with high ohmic resistance, to the output of a comparator.

3. A photo-printing machine according to claim 2, in which the capacitor of the control value forming device is followed by an amplifier of which the output is connected to one input of the comparator, the other input of which is connected to the input of the control value forming device.

4. A photo-printing machine according to claim 1, in which the transfer regulator is coupled to, and controlled by, the drive for the material to be reproduced.

5. A photo-printing machine according to claim 1, in which a brake device for the drive is controlled by the control value signal, for the purpose of bringing the speed of the drive of the material to be reproduced to a new and lower control value.

6. A photo-printing machine according to claim 1, in which an amplifying circuit having selectable different degrees of amplification is interposed between the measuring station and the control value forming device.

7. A photo-printing machine according to claim 6, in which the amplifying circuit comprises an amplifier, and a plurality of different resistors which are arranged to be switched in as desired in parallel with the aamplifier.

8. A photo-printing machine according to claim 7, in which there are additionally actuating elements for sets of diaphragms in the path of the measuring light, the actuating elements being arranged to be energized on the switching in of the resistors. 

1. A photo-printing machine for printing copies of varying sizes from originals of correspondingly varying sizes, including a measuring station having a photo-sensitive device for measuring the transparency of an original to be printed, a control value forming device and first store including a capacitor connected via an electronic valve to the photo-sensitive device of the measuring station to generate a control value signal, a second store for receiving a signal from the first store, an exposure station for exposing material to be reproduced, a drive for moving the material through the exposure station, a control circuit for the drive, arranged under the control of the stores to vary the drive speed in accordance with a control value signal in the second store, and a transfer regulator arranged to transfer a signal from the control value forming circuit and first store to the second store, when the material to be reproduced enters the exposure station.
 2. A photo-printing machine according to claim 1, in which the electronic valve is a MOSFET of which the control electrode is connected via a separating transformer, with high ohmic resistance, to the output of a comparator.
 3. A photo-printing machine according to claim 2, in which the capacitor of the control value forming device is followed by an amplifier of which the output is connected to one input of the comparator, the other input of which is connected to the input of the control value forming device.
 4. A photo-printing machine according to claim 1, in which the transfer regulator is coupled to, and controlled by, the drive for the material to be reproduced.
 5. A photo-printing machine according to claim 1, in which a brake device for the drive is controlled by the control value signal, for the purpose of bringing the speed of the drive of the material to be reproduced to a new and lower control value.
 6. A photo-printing machine according to claim 1, in which an amplifying circuit having selectable different degrees of amplification is interposed between the measuring station and the control value forming device.
 7. A photo-printing machine according to claim 6, in which the amplifying circuit comprises an amplifier, and a plurality of different resistors which are arranged to be switched in as desired in parallel with the aamplifier.
 8. A photo-printing machine according to claim 7, in which there are additionally actuating elements for sets of diaphragms in the path of the measuring light, the actuating elements being arranged to be energized on the switching in of the resistors. 